The present invention relates to a medium with information recorded on it (hereinafter called an information-recorded medium) and a method for reading the information. More particularly, the invention is directed to an information-recorded medium in card or other forms, which is virtually protected against an improper use, and a method for reading the information.
Information-recorded card media built up of a card substrate and a magnetic recording layer for recording information for identifying them have found wide application in the form of various cards such as ID cards, credit cards and bank cards.
A serious problem with currently available credit cards, bank cards, prepaid cards, securities, bank notes, passports, etc., are that they are easily forgeable, especially because it is relatively easy to overwrite or read the information on the magnetic layers, and so it has been proposed to laminate not-easy-to-produce holograms on the surfaces of cards for the purpose of preventing falsification. This is intended to prevent forgery by making use of the fact that holograms are not easy to produce and so the preparation of holograms themselves is costly. For instance, magnetic cards, when having hologram sheets thereon, can be visually shown not to be forgeries.
For another means for preventing the forgery of cards, etc., techniques for using magnetically recorded information in combination with otherwise recorded information, thereby judging whether they are true or not, have been proposed as well. According to one of these techniques, for instance, a magnetic recording layer with one information already recorded thereon is provided with another information in the form of a pattern composed of infrared absorbing and reflecting layers. That pattern is read due to a difference in the reflectivity with respect to infrared rays, thereby judging whether the card is true or not. According to this technique, the pattern composed of infrared absorbing and reflecting layers do not reflect visible light; the card has a very little chance of being forged, because the second information itself cannot easily be found, nor is it visible to the eye.
In a conventional information-recorded medium having a hologram laminated on the surface of a magnetic card substrate, however, it is general to identify the holographic information visually. Especially in the case of a reflection type hologram, the underlying layer of the hologram cannot be viewed from above: in other words, another information cannot be superimposed on that portion for recording.
When information other than holographic information is to be recorded on the magnetic recording layer while it is superimposed on the hologram, the amount of available information is limited, and card design becomes aesthetically poor. A grave problem with a conventional hologram is that it has still not a few chances of being forged, because it can be shown to be the very thing at the first glance, and moreover can be easily discerned in terms of in what form the information is recorded on the hologram. A serious problem when printable information and holographic information are recorded on the same region in a superimposed manner is that not only is it difficult to selectively separate one information from another for identification, but it is also difficult to identify each information with the use of a sensor, etc.
The combined use of magnetically recorded information and otherwise recorded information is not any essential solution to the problem, because the magnetically recorded information is still easy to forge.
In use, those cards are required to be identified as to they are genuine or not. For this purpose, hologram sheets have been laminated on the surfaces of the magnetic layers, as mentioned above. However, this is done to apply aesthetic effects to the cards, rather than to ensure that they can be identified due to the presence or absence of the holographic sheets. Therefore, if holograms--which have a problem with their production--are anyhow prepared and laminated on cards, there is then left a possibility that the cards may be easily forged by the overwriting of the magnetically recorded information. Thus, there is a strong demand for a card-identifying way of giving much higher security against some possible forgery or falsification.